Everything renders fine until looking at a somewhat large number of mobs (issue begins when looking at around 19-21 mobs on screen). I look away from my rainbow sheep/cow pen, and everything is normal. The second I look at the pen, it flickers everything from lava pools to bedrock to void. The flickers can be oriented normally or they can be at any angle in between.

I killed a significant number of mobs and it helped for a day, now it's back to being really bad again.